Agriculture Reference
In-Depth Information
mechanized ecological approach is cumulative over seasons and buffered
against weed patchiness and uncertainty by crop vigor, low weed levels, and
the use of a diversity of practices.
A third approach applies the ecological cropping systems practices men-
tioned above like green manures, intercropping, and rotations, but uses hand
tools, sometimes animal power, and only occasionally, if at all, tractor-drawn
implements. This represents an extension of traditional smallholder agricul-
tural systems, which are well suited to the localized management of weed
patchiness. The close interaction between mental and manual labor and the
speed at which work takes place permits continuous interpretation of field
and crop conditions and simultaneous adjustment of how each practice is
carried out. Farmers hand-weeding a field can observe local variation in both
crop stand and weed severity and simultaneously customize their manage-
ment plan to patchiness. Roguing primarily noxious weeds before they
produce seed, planting cover crops in large gaps in the crop stand, and selec-
tively applying mulch in potentially severe weed patches are examples of
mosaic weed management in response to weed patchiness.
Crop production based on the deliberate and opportunistic adaptation to
site heterogeneity still characterizes some indigenous agriculture (Richards,
1985; Salick,1989) and home gardens,but has diminished among many small
farmers who frequently use uniform, field-wide practices in spite of high
within-field variability.Their ability to innovate has been overloaded in many
rural communities by rapid social and economic displacement, shrinking
farm size, and accumulated land degradation (Blaikie, 1987, pp. 117-37). In
addition, local perspectives on how to innovate in crop production and weed
control have been sidetracked by input-linked credit programs and promo-
tion activities of the commercial input sector (van der Ploeg, 1993).
Bean production in Central America in a slash-mulch short-fallow rotation
illustrates the management of vegetation heterogeneity for improved crop-
ping. In this system bean seed is thrown into standing one- to three-year
fallow vegetation, which is then slashed as mulch to promote bean germina-
tion and control weeds. No further weeding is used. This system is low cost,
has low labor requirements,and is soil conserving,but has also been criticized
as low yielding (Thurston et al ., 1994).Farmers using this system readily iden-
tified good (e.g., Ageratum conyzoides , Melinis minutiflora , Melanthera aspera ) and
undesirable (e.g., Rottboellia cochinchinensis , Pteridium aquilinum ) fallow species
(G. Melendes, unpublished data). A shift to tillage and fertilizer and pesticide
inputs increased cropping frequency and yields, but cost more for inputs,
required more labor,and was not feasible on sloping lands.Upgrading fallows
by planting patches of Tithonia diversifolia or vining legumes like Canavalia
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